The objective of this proposal is to study the changes in microbial composition of dental plaque during its longitudinal development and to determine some of the principles which may govern these changes. Plaque samples will be removed from supragingival, mid pocket and advancing front sites of patients with advanced periodontitis and supragingival and deep sites of patients with mild periodontitis. Samples will be taken at 6, 2 and 0 weeks before extensive debridement of the pocket site and at 2, 6, 12, 24 and 52 weeks after treatment. The samples will be removed by means of an oxygen free gas flushed syringe, and dispersed, diluted and plated using continuous anaerobic techniques. The predominant cultivable microbiota from each site at each time period will be extensively characterized as previously described. The results of the study should give insight into the nature of the microbial composition of subgingival plaque and the sequence of microbial recolonization after its removal. Vibrios and "corroding" bacteria have been found in high numbers in a number of pathological sites in the oral cavity including destructive periodontal disease. Many members of this group fail to fit current classification schemes. Approximately 100 isolates will be extensively characterized using biochemical tests, end product analysis, ultrastructural examination and determination of the moles percent G plus C in their isolated DNA. Data collected will be computer coded and analyzed by cluster analysis as well as by other means. One of the principles which may govern the ecology of subgingival plaque is a dependence of certain groups of microorganisms on hydrogen evolution by other bacteria. Organisms will be sought in plaque which require hydrogen for growth. Attempts will be made to identify such organisms and enumerate both the hydrogen evolving and hydrogen utilizing organisms in dental plaques taken from sites exhibiting different disease states.